218Applications
Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic
applications. It is used in some thermometers, especially ones which are used to measure high
temperatures. A still increasing amount is used as gaseous mercury in fluorescent lamps, while
most of the other applications are slowly phased out due to health and safety regulations and is in
some applications replaced with less toxic but considerably more expensive Galinstan alloy.
Medicine
Mercury and its compounds have been used in medicine, although they are much less common
today than they once were, now that the toxic effects of mercury and its compounds are more
widely understood. The element mercury is an ingredient in dental amalgams. Thiomersal (called
Thimerosal in the United States) is an organic compound used as a preservative in vaccines,
though this use is in decline. Another mercury compound Merbromin (Mercurochrome) is a topical
antiseptic used for minor cuts and scrapes is still in use in some countries.
Since the 1930s some vaccines have contained the preservative thiomersal, which is metabolized
or degraded to ethyl mercury. Although it was widely speculated that this mercury-based
preservative can cause or trigger autism in children, scientific studies showed no evidence
supporting any such link. Nevertheless thiomersal has been removed from or reduced to trace
amounts in all U.S. vaccines recommended for children 6 years of age and under, with the
exception of inactivated influenza vaccine.
Mercury in the form of one of its common ores, cinnabar, is used in various traditional medicines,
especially in traditional Chinese medicine. Review of its safety has found cinnabar can lead to
significant mercury intoxication when heated, consumed in overdose or taken long term, and can
have adverse effects at therapeutic doses, though this is typically reversible at therapeutic doses.
Although this form of mercury appears less toxic than others, its use in traditional Chinese medicine
has not yet been justified as the therapeutic basis for the use of cinnabar is not clear.
Today, the use of mercury in medicine has greatly declined in all respects, especially in developed
countries. Thermometers and sphygmomanometers containing mercury were invented in the early
18th and late 19th centuries, respectively. In the early 21st century, their use is declining and has
been banned in some countries, states and medical institutions.
In 2002, the U.S. Senate passed legislation to phase out the sale of non-prescription mercury
thermometers. In 2003, Washington and Maine became the first states to ban mercury blood
pressure devices. Mercury compounds are found in some over-the-counter drugs, including topical
antiseptics, stimulant laxatives, diaper-rash ointment, eye drops, and nasal sprays.
The FDA has "inadequate data to establish general recognition of the safety and effectiveness", of
the mercury ingredients in these products. Mercury is still used in some diuretics, although
substitutes now exist for most therapeutic uses.
Production of Chlorine and Caustic Soda
Chlorine is produced from sodium chloride (common salt, NaCl) using electrolysis to separate the
metallic sodium from the chlorine gas. Usually the salt is dissolved in water to produce a brine. By-
products of any such chloralkali process are hydrogen (H 2 ) and sodium hydroxide (NaOH), which
is commonly called caustic soda or lye. By far the largest use of mercury in the late 20th century
was in the mercury cell process (also called the Castner-Kellner process) where metallic sodium is
formed as an amalgam at a cathode made from mercury; this sodium is then reacted with water to
produce sodium hydroxide. Many of the industrial mercury releases of the 20th century came from
this process, although modern plants claimed to be safe in this regard.